ALUMINA. 
349 
Fig. 340. 
Fig. 341. 
Fig. 342. 
Rockland County. At Pier- 
montj apophyllite occurs in the 
greenstone, but it has not hitherto 
been obtained in well defined crys¬ 
tals. Figs. 340, 341 and 342 repre¬ 
sent the forms which have been 
observed in the same formation at 
Bergen hill, New-Jersey. M on 
M 90° ; P on M 90° ; P on s 120° 
5'; M on s 128° 20' ; sons 104° 
18'. 
PREHNITE. 
(In honour of its discoverer, Col. Prehn.) 
Prehnite. Haiiy, Cleaveland, Phillips, Thomson, Shepard and Bcudant. — Axotomous Prehnite. Jameson. — 
Axotomer Triphan-Spath. Mohs. 
Description. Colour commonly green of various shades, but sometimes grey and white. 
It occurs regularly crystallized ; also in scopiform, stellular and fibrous 
concretions, and massive. The primary form is a right rhombic 
prism. Fig. 343. M on M 7 100° (Phillips), 102° 30' ( Beudant ). 
Cleavage distinct parallel to P ; less so, parallel to M. Fracture un¬ 
even. Lustre vitreous, except on the face P, which is pearly. Ranges 
from transparent to translucent. Hardness from 6.0 to 7.0. Specific 
gravity from 2.90 to 2.95. When heated, it becomes electric. By 
calcination, it yields water. Before the blowpipe, it melts into a white, greenish or pale 
yellowish frothy glass ; with borax, it forms a transparent bead. Slowly soluble in muriatic 
acid, from which solution an abundant precipitate is produced by oxalate of ammonia. 
Prehnite has a lower degree of lustre than stilbite or heulandite, which it sometimes re¬ 
sembles. It does not, like many of the zeolite family, form a jelly with acids. By calcina¬ 
tion, it yields less water than chabazite or epistilbite. 
Composition. Silica 43.60, alumina 23.00, lime 22.33, oxide of iron 2.00, water 6.40 
( Thomson ). 
Geological Situation. This mineral usually occurs in primitive rocks, or in trap and 
greenstone. It is found in both these situations in this Slate. 
LOCALITIES. 
Essex County. Prehnite occurs massive and semi-crystallized, and of a yellowish white 
Fig. 343. 
